As is well known to those skilled in this art, the most efficient compressor operation is one where the centrifugal compressor operates as closely as possible to the surge line without actually going into surge. Quite apart from the efficiency aspect, however, it is also well known that a surging compressor results in excessive vibration and possibly destructive damage.
There are numerous systems in the prior art for control of the flow of gases in a recyle line connected between the discharge and intake of a centrifugal compressor for the purpose of positively preventing the compressor from going into surge. U.S. Pat. No. 3,292,846 dated Dec. 20, 1966, shows a control system of this type in which flow in the recycle line is made responsive to density of the discharge gas and the speed of the compressor to maintain a sufficient flow through the compressor to prevent surging thereof.
Another prior U.S. Pat. No. 3,876,326 dated Apr. 8, 1975, utilizes a computer controlled bleed valve connected to an intermediate stage of the compressor. Computer inputs in this system include speed of the compressor shaft, input horsepower, and inlet and outlet parameters of the gas flow.